JP2009107890A - Glass flow path, apparatus for manufacturing glass, and method of manufacturing glass - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flow path for simply obtaining high quality glass molded body of a recent high refractive glass or low softening temperature glass which is difficult to select molding conditions by averaging a flow rate or a temperature distribution to reduce occurrence of striae or devitrification in the glass flow path of the glass manufacturing apparatus which usually has a tendency that the flow rate in the vicinity of the center is made higher and to provide the flow path in which the flow rate or the temperature distribution is simply controlled even in a short distance in the conventional glass to make the apparatus small-sized. <P>SOLUTION: The flow path is connected to a molten glass tank to allow molten glass to flow out and is divided into a plurality of regions by two or more partitioning plates. In each of the partitioning plate, a slit for passing the glass stream is provided and directions of the slits of the adjacent partitioning plates differ from each other. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a technique for manufacturing a predetermined amount of a glass molded body, and particularly to a technique for manufacturing an optical glass molded body.

  In recent years, in the field of optical devices such as digital cameras and projectors, there has been a demand for miniaturization and weight reduction, and accordingly, there is an increasing demand for aspheric lenses that can reduce the number of lenses used.

In general, the lenses constituting the optical system generally include a spherical lens and an aspheric lens. Many spherical lenses are manufactured by grinding and polishing a glass molded product obtained by reheat press molding a glass material. On the other hand, an aspheric lens is a method in which a heat-softened preform is press-molded with a mold having a high-precision molding surface, and the shape of the high-precision molding surface of the mold is transferred to a preform material, that is, It is mainly produced by precision press molding.

  As a precision press-molding preform, a spherical, elliptical or flat glass molded body (glass gob) is often used. It can be manufactured by allowing it to flow out from a connected nozzle or the like onto a mold, forming it into plate-like glass or rod-like glass, and further cold-working them. In recent years, molten glass that flows out from a flow path such as a nozzle is cut by a shear or separated by using surface tension, and flows down (drops) onto a porous mold that ejects gas, for example, and then floats. A technique for adjusting the glass gob to an appropriate size and shape by molding is used. However, in the former case, traces of cutting by the shear may remain on the glass gob, so in recent years the latter is often used.

In any of the above means, when glass is caused to flow out of the flow path, in order to control the temperature and flow rate of the glass flow, or to prevent defects such as striae and devitrification occurring during molding, Various shapes have been devised for the flow path. In recent years, various methods have been devised to cope with the increase in liquid phase temperature, the decrease in viscosity due to the improvement of optical glass represented by higher refractive index, etc., or the decrease in viscosity due to lower temperature softening. However, the current situation is not enough.

  In Patent Document 1, the diameter of the outlet is made larger than the diameter of the channel main body, for example, the molten glass outlet at the end of the channel is opened in a tapered shape so that the molten glass flow is longer than the channel outlet. Nozzles are described that can be held for a period of time to delay the timing of glass flow.

  In Patent Document 2, when molten glass starts to flow from a melting apparatus, passes through a pipe, and flows out from an outlet, the flow velocity distribution is made uniform by adding a constriction inside, and the modified glass in which the components are volatilized is disclosed. A method is described that suppresses retention and prevents striae. In addition, it is described that the temperature of the throttle portion is controlled to be higher than that other than the throttle portion in order to prevent the flow rate from being reduced due to the throttle.

  Patent Document 3 describes a method in which a resistance member is provided inside a flow path to reduce the flow velocity of the glass flow flowing through the center of the cross section of the flow path and increase the maximum weight of the glass gob that can be obtained.

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JP-A-10-36123 JP 2003-306334 A JP-A-8-26737

However, the above conventional methods have the following problems.

In general, when molten glass is flowed out of a melting tank through a flow path and molded with a molding die, temperature control is performed by gradually decreasing the temperature from the melting tank to the outlet, and a temperature suitable for molding. It is necessary to lower the molten glass temperature. Here, for example, striae derived from the volatilization of the glass component may occur after the outflow, but in this case, it is necessary to cope with this by lowering the flow path control temperature. Due to the heat radiation from the outer wall of the flow path, the temperature of the glass in the nozzle is lower near the inner wall surface and higher near the center of gravity of the flow path cross section. Since the viscosity of the glass increases as the temperature decreases, the flow velocity distribution of the glass in the cross section of the flow path is low near the inner wall surface and is high near the center of gravity of the cross section.

  When the temperature of the flow path wall is fed back and controlled in order to set the temperature of the glass flow in the flow path to an appropriate value, the measured temperature at the flow path wall represents the glass temperature near the inner wall surface almost accurately. However, it shows a low temperature deviating from the glass flow center temperature (that is, the temperature of the glass flow passing near the center of gravity of the cross section of the flow channel in the flow channel). Therefore, in a glass having a high liquidus temperature, if the glass flow center is controlled to a temperature at which volatilization does not occur, the glass temperature in the vicinity of the inner wall of the flow path decreases to a crystal growth temperature, a so-called devitrification temperature. Occurrence of see-through may occur.

In the flow path described in Patent Document 1, since the outlet is tapered and the inner diameter is increased, the temperature difference and the flow velocity difference between the inner wall surface and the glass flow center are increased, and the above-described tendency is more prominent. Become.

When a flow path having a restriction as in Patent Document 2 is used, there is an effect of uniforming the flow velocity distribution of the glass flow, but a high temperature glass flow near the center of gravity of the cross section of the flow channel is taken out. Sometimes it is difficult to prevent striae from volatilization. If the control temperature is lowered to suppress volatilization, devitrification is likely to occur and grow immediately, thereby blocking the flow path of the throttle portion, and the outflow itself is likely to stop. In the example, in order to suppress the flow rate drop due to the restriction, the temperature of the restriction part is set to a temperature higher than that other than the restriction part, and it is clear that this is not a method suitable for the production of high refractive index glass in recent years. .

  The flow path described in Patent Document 3 delays the flow rate of the molten glass at the center by a resistance member provided at the center of the inside, and the velocity distribution of the outflow rate is made uniform, but the heat capacity In a small resistance member mainly composed of a small noble metal, the glass flow center temperature immediately becomes high. Therefore, the effect of lowering the glass flow center temperature cannot be obtained, and there is no effect of suppressing striae derived from volatilization. Further, as shown in FIG. 3 in Patent Document 3, it is necessary to fix the resistance member using a support member, and it is extremely difficult to process the glass outlet channel mainly containing a noble metal such as platinum. Further, in claim 4 of Patent Document 3, a plurality of flow paths are provided at the bottom of the crucible, and tip ends of the plurality of flow paths are connected to each other to form one flow path opening. However, the high temperature glass flow is generated at the center of each of the plurality of flow paths, and the effect of lowering the glass flow center temperature flowing down cannot be obtained. Applying such a complicated structure makes it very difficult to change the structure to adapt to the temperature, viscosity, wetting, density, and fluid pressure of the glass, which also complicates the flow rate and temperature distribution. However, a simpler structure was sought.

  In the present invention, the occurrence of striae and devitrification is usually reduced by averaging the flow velocity in the glass flow path where the flow velocity near the center tends to increase. As a result, the present invention provides a flow path for obtaining a glass molded body of recent high refractive glass or low temperature softened glass that is very difficult to select molding conditions in a simple and high quality manner. It is another object of the present invention to provide a flow path that enables simple and short-distance control even in conventional glass, and that can reduce the size of the apparatus.

The inventor divides the flow path into a plurality of regions by two or more partition plates installed substantially perpendicular to the flowing direction of the molten glass, and the partition plates are provided with slits for allowing the glass flow to pass and adjacent to each other. By making the slit directions of the partition plates different from each other, in addition to averaging the temperature / flow velocity distribution, the desired temperature / flow velocity distribution can be obtained, and as a result, the disadvantages such as striae can be suppressed. We found out what we can do and came to solve the above problems.
Specifically, the present invention has the following configuration.

(Configuration 1)
A flow path connected to the molten glass tank and allowing the molten glass to flow out,
Partitioned into a plurality of regions by two or more partition plates installed substantially perpendicular to the outflow direction of the molten glass, the partition plate is provided with a slit for passing the glass flow,
The said flow path characterized by the direction of the slit of the said adjacent partition plate differing mutually.
(Configuration 2)
The flow path according to Configuration 1, wherein the direction of the slits of the adjacent partition plates is different by 30 degrees or more.
(Configuration 3)
The flow path according to Configuration 1 or 2, wherein an aspect ratio of the slit is 1.8 or more.
(Configuration 4)
4. The flow path according to any one of configurations 1 to 3, wherein the number of slits provided per sheet of the partition plate is 1 to 5.
(Configuration 5)
6. The flow path according to any one of configurations 1 to 5, wherein a width of the slit is ½ or less with respect to a maximum width of a cross-sectional shape of the flow path perpendicular to the glass flow.
(Configuration 6)
The glass manufacturing apparatus which has a flow path in any one of composition 1 to 5.
(Configuration 7)
A method for producing a glass molded body, comprising melting a glass raw material in a melting tank, and flowing a molten glass flow into a mold through a nozzle connected to the melting tank to form a glass molded body. The manufacturing method including a step of averaging the temperature distribution in the flow path by passing any of the flow paths through the flow paths of configurations 1 to 4.

  Hereinafter, the flow path of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present invention. .

In the present invention, the “flow path” is connected to a melting tank for melting and / or holding molten glass, and the entire flow path and flow path through which the glass flow passes when the molten glass flows out into a mold (for example, a mold). It is a concept that includes an exit. That is, it is a concept that encompasses so-called pipes, orifices, and nozzles. Further, the “channel cross section” refers to a space-shaped cross section in which the molten glass in the flow channel flows, and the “channel cross section” refers to a space-shaped cross section in which the members constituting the flow channel and the molten glass flow.

Normally, the temperature control of the flow path is also performed by various methods, but the temperature distribution of the molten glass flowing through the flow path is near the center of gravity of the cross section of the flow path (in the case of a substantially circular cross section, the center of the cross section direction) Is the highest, so the flow rate is high.
As described above, in the present invention, the flow path is divided into a plurality of regions by two or more partition plates installed substantially perpendicular to the flowing direction of the molten glass, and the partition plate is used for passing the glass flow. By providing slits and making the direction of the slits of the adjacent partition plates different from each other, the gap due to the temperature distribution and the position of the flow velocity is to be relaxed.

FIG. 1 is an example showing the flow path of the present invention. As shown in FIG. 1, the partition plate 1 is preferably in contact with the inner wall of the flow path 2. However, the installation method is not particularly limited, and it may be installed by welding, or may be a fitting type by performing a process such as providing a groove on the inner wall of the flow path. If it is a built-in type, the partition plate can be appropriately changed depending on the type of glass to be melted.

The material of the partition plate 1 is not particularly limited, but it is necessary to have both heat resistance and strength sufficient to withstand the thermal load and pressure load of the molten glass flow. Therefore, it is preferable to use a known platinum alloy, a reinforced platinum alloy in which a reinforcing material is dispersed, or a gold-containing reinforced platinum alloy with improved wettability.

The entire periphery of the partition plate is preferably in contact with the inner wall of the flow path. This is because if there is a gap between the periphery of the partition plate and the inner wall of the flow path, the effect of holding the partition plate is reduced and deformation is likely to occur.

The partition plate 1 is preferably provided with slits for passing the molten glass flow, and the directions of the slits of the adjacent partition plates are preferably different from each other. By providing the slits in this way, turbulent flow is generated, and the slits of the adjacent partition plates are made in different directions, so that the stirring effect of the glass flow in the flow path is dramatically increased, and the temperature in the cross section of the flow path is increased. In addition to averaging the flow velocity distribution, the desired temperature / flow velocity distribution can be obtained.
In order to further enhance the stirring effect, the direction of the slits of adjacent partition plates is preferably different by 30 degrees or more, more preferably 45 degrees or more, and most preferably 90 degrees. Here, the direction of the slits of the adjacent partition plates is an angle formed by the directions of the two straight lines that maximize the distance between the two straight lines when the slits of the adjacent partition plates are sandwiched between the two parallel straight lines. It takes a range of degrees to 90 degrees. When there are a plurality of slits in one partition plate, the one having the largest angle is selected.

Moreover, in order to further enhance the stirring effect by changing the direction of the slits of the adjacent partition plates, the aspect ratio of the slit shape is preferably 1.8 or more, more preferably 1.9 or more. Preferably, it is 2.0 or more.
The shape of the slit is not particularly limited, but an ellipse, a rectangle and the like are preferable.
Here, the aspect ratio of the slit shape means that when the slit shape is sandwiched between two parallel straight lines, the distance where the distance between the two straight lines is the largest is L, and the distance where the distance between the two straight lines is the smallest is l. , L / l.

The number of slits provided per partition plate is 1 or more, and if it is more than necessary, the effect of stirring the glass flow cannot be obtained sufficiently, preferably 5 or less, and more preferably 4 or less. Most preferably, it is 3 or less. In order to further enhance the stirring effect of the present invention, when there are a plurality of slits provided on one partition plate, the slits are preferably parallel.

In order to further enhance the stirring effect of the glass flow in the flow path, the width of the slit is preferably 1/2 or less with respect to the maximum width of the cross-sectional shape of the flow channel perpendicular to the glass flow, and is 1 / 2.5 or less. Is more preferable, and 1/3 or less is most preferable. On the other hand, if the width of the slit is narrower than necessary, the flow of the glass flow deteriorates, and devitrification is likely to occur. Therefore, the width of the slit is preferably 1/30 or more, more preferably 1/20 or more, and most preferably 1/15 or more with respect to the maximum width of the channel cross-sectional shape perpendicular to the glass flow.
Here, the maximum width of the channel cross-sectional shape perpendicular to the glass flow is a value at which the distance between the two straight lines becomes maximum when the channel cross-sectional shape perpendicular to the glass flow is sandwiched between two parallel straight lines.

If the area of the slit provided per partition plate is larger than necessary, the effect of stirring the glass flow is likely to be reduced, and if it is smaller than necessary, the flow of the glass flow is deteriorated and devitrification is likely to occur. Therefore, the total area of the slits provided per partition plate is preferably 10% or more, more preferably 15% or more, most preferably 20% or more, preferably 90% or less of the flow path cross-sectional area. More preferably, it is 85% or less, and most preferably 80% or less.

The installation position of the partition plate is not particularly limited, but each position is determined in consideration of the thermal conductivity, heat capacity, flow path diameter, flow rate, desired temperature / temperature distribution, and the like of the glass. Although it naturally depends on the total length of the flow path, if it is too upstream, a new flow velocity distribution is likely to be generated even if the flow velocity distribution is once averaged, and it is difficult to obtain the effect expected in the present invention. Therefore, it is preferable to have the partition plate in a range of 50% downstream, more preferably 45% downstream, and most preferably 40% downstream with respect to the total length of the flow path.

The flow path of the present invention does not hinder heating and / or cooling by the flow path itself and / or external addition means. As the heating of the channel itself, a known heating method by directly energizing the channel can be used, and as an external addition means, a known method such as a gas burner, an electric heater, infrared radiation, high frequency heating or the like can be used. You may use suitably. Further, by covering the vicinity of the glass outlet with a ring burner or the like and keeping it warm, defects such as devitrification and striae can be further suppressed.

  By applying the flow path of the present invention to a known glass production apparatus, a high-quality optical glass molded body free from striae or the like can be obtained.

The glass forming means using the flow path of the present invention is not particularly limited. As optical glass molding, it may be continuously flown out as a glass flow into a mold, and may be continuously molded into a plate-like or rod-like glass, etc., or the glass gob is separated by shear or surface tension, and on a porous mold. A glass gob may be formed by floating molding.

As the material of the flow path of the present invention, materials usually used in the glass melting process can be used, for example, platinum, reinforced platinum, gold, reinforced gold, rhodium, other noble metals and their alloys, or quartz. Can be used. Further, a material plated by a known method, for example, platinum having a gold-plated inner surface or a ceramic film such as SiC may be used.

Since the present invention defines the internal structure of the flow path, the atmosphere in the vicinity of the flow path outlet may be appropriately changed. For example, a nitrogen atmosphere or an inert gas atmosphere such as argon may be used. In some cases, the channel outlet may be covered with a heated atmosphere.

Specific examples of the present invention will be described below.

Example 1
In this example, the optical glass is melted in a platinum crucible, and the molten glass is caused to flow out from its outlet through a flow path connected to the crucible. The glass gob for use as a precision press-molding preform was obtained.

As the flow path, a reinforced platinum flow path having the same shape as that shown in FIG. 3 was used. Here, the inner diameter of the flow path is 3 mm (the cross-sectional area of the flow path is 7.07 mm ² ), and the outlet is expanded to 6 mm. The total length of the channel, that is, the length from the outlet of the crucible to the outlet at the end of the channel was 2 m.

The partition plate in the flow path was attached at a point of 50 mm and 55 mm from the outlet to the crucible, and the thickness of the partition plate was 1 mm. The slits were rectangular, provided in parallel at two locations on the partition plate, the width was 0.4 mm, and the length was 2.2 mm. The direction of the slit of the adjacent partition plate was 90 degrees. The area of the cross section of the glass flow path at the part where the partition plate was attached was 1.76 mm ² . That is, the flow path cross-sectional area where the partition plate was installed was about 24.9% of the place where the partition plate was not installed.

The receiving mold was made of porous stainless steel, and received molten glass in a state where air was blown from the receiving surface thereof. Thus, the molten glass floated from the receiving mold to receive glass gob.

The glass used was melted optical glass mainly composed of boron oxide and lanthanum oxide. The crucible was kept at about 1200 ° C., and the flow path was kept at about 1100 ° C. by energization heating. From the outlet, the molten glass was separated into droplets. The amount of molten glass flowing out at this time was 80 g per minute.

  When this glass gob was visually observed for optical defects such as devitrification and striae, such a defect could not be found, and it was a high-quality glass gob that could be used as a preform for molding an optical element.

It is a principal part conceptual diagram of the flow path of this invention. It is a principal part conceptual diagram which shows the other aspect of the flow path of this invention.

Explanation of symbols

1 Partition plate 2 Flow path 3 Slit

Claims (7)

A flow path connected to the molten glass tank and allowing the molten glass to flow out,
Partitioned into a plurality of regions by two or more partition plates installed substantially perpendicular to the flowing direction of the molten glass, the partition plate is provided with a slit for passing the glass flow,
The said flow path characterized by the direction of the slit of the said adjacent partition plate differing mutually.   The flow path according to claim 1, wherein the direction of the slits of the adjacent partition plates is different by 30 degrees or more.   The flow path according to claim 1 or 2, wherein the slit has an aspect ratio of 1.8 or more.   The flow path according to any one of claims 1 to 3, wherein the number of slits provided per sheet of the partition plate is 1 to 5.   The flow path according to any one of claims 1 to 5, wherein a width of the slit is ½ or less of a maximum width of a cross-sectional shape of the flow path perpendicular to the glass flow.   The glass manufacturing apparatus which has a flow path in any one of Claims 1-5.   A method for producing a glass molded body, comprising melting a glass raw material in a melting tank, and flowing a molten glass flow into a mold through a nozzle connected to the melting tank to form a glass molded body. The said manufacturing method including the process of averaging the temperature distribution in a flow path by letting a flow path in any one of Claims 1-4 pass.

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